January 24th, 2011

Did You Know That Everyone Has 2 Family Trees?

It’s true, we all have two family trees. – a genetic family tree and a genealogical family tree!  Let me explain.

I recently spoke with a friend who attended a genealogical convention in Dublin, Ireland. This person had undergone DNA testing which compared his DNA with that of another person who he suspected might be related to him. It turned out that their DNA’s matched on 99% of Y-DNA markers; yet even though they suspected that they were third cousins, neither of them could find evidence of the other in their family histories. Even though their DNA was almost identical, it appeared they may not be related at all. My friend approached a well known genealogist and asked him about a possible explanation. I was, and you may well be, surprised at the answer he was given.

The Explanation

My friend had used Family Tree DNA’s Surname Project, and the first thing the expert explained was that; just because two people don’t have any DNA in common within the Family Inheritance section of Family Tree DNA, or if they can’t locate each other in the website’s Projects, this doesn’t mean that they are not related. What it does point to is that the people involved shared a common male ancestor (revealed by the DNA Y-Markers they had in common), but not any other DNA.

Because DNA is passed from generation to generation randomly, the entire genetic makeup of a parent is not completely passed on to the child. This means that certain components or parts of that DNA are lost in subsequent generations. In an attempt to make this clearer, the professional genealogist went on to explain that cousins will only share DNA if they have inherited the same random components from their common ancestors. As you can imagine the probability of that occurring decreases with each generation.

My friend and the other individual who was tested believed that they were third cousins. This meant that they only had two of sixteen ancestors in common through four generations. In their case it seemed that they did not randomly inherit any common DNA from those two ancestors. It is possible however that they inherited different components from those two common ancestors, but they wouldn’t appear as a match on Family Tree DNA because the same segment of DNA is required for that.

It must be stated at this point that the DNA testing on Family Tree DNA compares only those bits of DNA that are submitted for testing. An entire DNA test, known as a Whole Genome test, is not readily available to consumers, yet that is the only analysis that can compare the entire DNA’s of different persons.

Our Two Family Trees

My friend was satisfied with this explanation, though still convinced that he was related to the other person involved. Why couldn’t they find each other within their respective family histories? This was the revealing answer we were given; turns out that in essence we all have Two Family Trees!

The first is our Genealogical Family Tree, which is the collection of recorded documentation of our family throughout the ages. There are several reasons why my friend and his “cousin” couldn’t find each other in their family history records. They are obviously related due to having a common male ancestor, but adoption, divorce, missing records, name changes, immigration, and many other circumstances could account for their dilemma. They’ll have to sort out whichever that is and come to terms with it, but without DNA testing they could have never been sure if they were related or not. That being confirmed, they can now move forward in their respective searches.

Our genealogical family tree also involves our biological history; every person within our family who gave birth to a child, who gave birth to a child, which eventually led to you. This is the family tree we are all familiar with, but apparently there is another which can reveal additional information – our Genetic Family Tree.

Because not everyone in our ancestral lineage contributed DNA to us (due to the random nature by which DNA is passed on), we all possess a second family tree – our genetic one. This contains every ancestor in our family lineage that has contributed DNA to our makeup. The increasing availability of genetic sequencing to the common populace will eventually make it possible to fully trace and construct our Genetic Family Trees similarly to how we now construct our genealogical ones.

The exciting developments within the science of DNA testing are opening up a whole new genealogical sphere. DNA samples from living people can now be used to determine the inheritance of DNA from ancestors who died centuries before. This is making it increasingly easier to determine ancestral connections and to find missing relatives, but also gives us more genealogical work to do – constructing our Genetic Family Trees. Better get to work!